In general, dot matrix printers can be separated into two types of printers--line printers and serial printers. Line printers include mechanisms for creating lines of dots substantially simultaneously as paper moves through the printers. A series of dots creates characters (or a design). Contrariwise, a serial dot matrix printer includes a head that is moved back and forth across the sheet of paper, either continuously or by steps. In the past, most such heads included a column of dot printing elements. As each column position of a character position is reached during printing the required number of dot printing elements are actuated to form dots. A series of dot columns creates a character (or part of a design). This invention is related to serial dot matrix type printers.
As noted above, in the past, most (but not all) print heads for serial dot matrix printers, have included a column of dot printing elements, usually seven or nine. Normally, the printing elements have taken the form of wires supported by guide members positioned so that one of the ends of the wires are arrayed in a column. The other ends of the wires are positioned so that the wires can be longitudinally moved by electromagnetically actuated drive mechanisms. In some instances, the other ends of the wires are attached to the movable element of the related electromagnetic drivers such that the wires are in retracted positions when the drivers are de-energized. In other instances, the wires are not permanently attached to the movable elements of the electromagnetic drivers. Rather, the wires are retracted to a withdrawn position by coil springs and the like when the related electromagnetic drivers are de-energized. Regardless of how assembled, when an electromagnetic driver is energized, the associated wire is moved longitudinally. Longitudinal movement creates a dot by pressing the "column" end of the wire against a ribbon that faces a piece of paper.
While serial dot matrix printers have been commercialized, prior art print heads used in serial printers have a number of disadvantages. For example, they are more complex and, therefor, less reliable, than desired. In addition, prior art serial dot matrix printer print heads require more actuating power than is desirable. For example, one such print head requires a linear ramp-up of current to about three (3) amps over a period of about six-hundred (600) mircroseconds. Obviously, this relatively high power draw requires that the coils of the electromagnetic actuators have a relatively large wire size in order to achieve an acceptable dot print head life in excess of several hundred million dot prints per printing element. Obviously, the use of relatively large wire increases the size and cost of the print head. Increased size, of course, increases the inertia of the head, whereby the head movement mechanism requires a relatively large driving power source. In addition to increasing costs, such prior art print head assemblies have the further disadvantage that their large power requirements emit large amounts of heat. As a result, large fans and the like are required to cool the head assemblies. Furthermore, those print heads that include wires mounted in guide members have the disadvantage that the guides and/or wires are subject to wear and, thus, frequent replacement.
Attempts have been made to overcome some of the foregoing disadvantages of print heads suitable for use in serial dot matrix printers by using permanent magnets, for example. In this regard, attention is directed to U.S. Pat. Nos. 3,592,311, 3,659,238, 3,672,482 and 4,037,704 as examples of prior art proposals to use permanent magnets in serial dot matrix printer print heads. For various reasons, such attempts have not been entirely successful. For example, they are still more complex than desired. Further, they are larger than desired. Proposals also have been made to use permanent magnets in line dot matrix printers. In this regard, attention is directed to U.S. Pat. Nos. 3,931,051, 4,033,255 and 4,044,668. Obviously line printers function in a different manner than serial printers. Thus, they have different design constraints, whereby technology that is useful in one type of printer is not necessarily useful in the other type of printer. For example, line printers of the type described in U.S. Pat. Nos. 3,941,051, 4,033,255 and 4,044,668 do not require that the dot printing elements be closely spaced together because the elements are oscillated across a character position. As a result, printing elements in the form of short pins, mounted on relatively wide hammers, can be used. Contrariwise, because serial printers have, in the past, required a column of closely spaced printing elements, the elements have taken the form of guided wires. Thus, different requirements have led to different structures being developed, and the foregoing observation that what will function in a line printer environment will not necessarily function in a serial printer environment and vice versa.
It is the object of this invention to provide a new and improved print head suitable for use in a serial dot matrix printer.
It is a further object of this invention to provide an uncomplicated print head for a serial dot matrix printer.
It is still a further object of this invention to provide a low-cost, inexpensive print head for a serial dot matrix printer.
It is yet another object of this invention to provide a print head suitable for use in a serial dot matrix printer that has substantially lower power requirements than prior art serial dot matrix printer print heads.